Real-Time Operating Systems for Embedded Computing

Real-Time Operating Systems for Embedded Computing

李姿宜 R909210452003,06,10

Outline

MotivationEmbedded operating systemsReal-Time operating systemsA case studyConclusion

Motivation

SoC CPU + ASIC + Software Traditional application-specific systems

Implemented by algorithm-to-architecture methodology.

Modern Trend : Design Reuse, which software plays an important role, and Real-time operating systems ( RTOS ) is the critical

component

Role of RTOS in HW/SW Co-Design

Formal Languages

Partitioning

HW SynthesisSW Synthesis

RTOS Tasks Logic Synthesis

Code Optimization Logic Optimization

Board Level Prototyping

Co-SimulationAnd

Formal Verification

A new system-level synthesis flow

System Design

RTOS

Process Management

Interprocess Communication

Memory Management

I/O Management

Algorithm Development

Compilation

Architecture IC Design

Embedded Operating System

Task Managementcreate, delete, suspend, resume

Time Managementsystem clock, generate delay

Inter Task Communication and SynchronizationMultitasking

No-OS disable interrupts / enable interruptsWith-OS enter/exit critical section

Embedded Operating System (cont’)

Inter Task Communication and SynchronizationWait for event, interruptExchange data, queues, shared memory

Memory Management temporary data buffersallocate, free (critical in ES)

Real Time Operating System

Embedded applications can and will respond to external events before deadline

Soft real-time requirements:Breaking the time limit is unwanted, but is not

immediately criticalHard real-time requirements

Breaking the limit is always seen as a fundamental failure

Real Time Operating System Characteristics

Bounded Interrupt ServicingPriority Based SchedulingPre-Emptive TasksScalability

Previous RTOS Research(1/2)

Scheduling of the CPU : Central purpose of and RTOSA complete process : waiting, ready, and

executingScheduling policies

Cooperative schedulerStatic priority-driven schedulerDynamic priority-driven scheduler

Previous RTOS Research(2/2)

Scheduling methodology examples Rate Monotonic algorithm by Liu & Layland

static priorities based on periods higher priorities to shorter periods

optimal among all static priority schemes

Earliest-deadline First dynamic priority assignment closer a task’s deadline, higher is it priority applicable to both periodic and aperiodic tasks need to calculate priorities when new tasks arrives

more expensive in terms of run-time overheads

Commercial RTOS Offerings

Integrated Systems (pSOS system), WindRiver (VxWorks), Microtec Research (VRTX), Microware Systems (OS-9), QNX (QNX), Lynx Real-Time system (LynxOS), Microsoft (Windows-CE)

Practical application issuesMemory requrimentContext switch time Interrupt latency

An example of Commercial RTOS

A Case Study

On-Chip Multimedia Real-Time OS LSIs such as digital signal processing,

image processing, and protocol processingTwo Major problems:

Overhead of Cyclic Task ExecutionMemory Capacity Limiation

Modeling of System LSIs

Core CPU MemoryHOST I/F

I/O

Block #A Block #B Block #C

Application specific hardware unit

Requirements of Embedded Software

Requirement Hardware control Scheduling Synchronization Urgent processing Memory capacity

Real-Time OS function

Task Management Multitasking Scheduling New cyclic task

Interrupt Management

Semaphore Management

Very small real time OS

On-Chip Multimedia Real-Time OS

Task management

Cyclic task is created and start

Cyclic task is deleted

Dedicated interval time

Cyclic task execution

Resource for task

Allocated

Resource for task

deleted

On-Chip Multimedia Real-Time OS

Cyclic task is created and start

Cyclic task is suspended

Cyclic task is resume

Cyclic task is deleted

Resource for task

Not deleted

Resource for task

Allocated

Resource for task

Not allocated

Resource for task

deleted

On-Chip Multimedia Real-Time OS

Interrupt ManagementSemaphore management

Conclusion

Made a survey of real-time OS for embedded system

Factors which influence the choosing of OS?The requirements of the applicationsThe special features of OSReal- Time constrained